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Posted: 6/29/2018 5:59:10 PM EDT
[#1]
I was going to mention piston weights have to be the same. If you’re doing this as a budget type thing go for it. There really isn’t any more risk in doing it this way or the “correct” way. Sometimes even a properly built engine will scatter due to some anamoly or oversight.
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Posted: 6/29/2018 6:01:16 PM EDT
[#2]
Quote HistoryQuoted:
I was going to mention piston weights have to be the same. If you're doing this as a budget type thing go for it. There really isn't any more risk in doing it this way or the "correct" way. Sometimes even a properly built engine will scatter due to some anamoly or oversight. Unless its an absolute budget build once you go through the effort for one side, you may as well do both cylinders |
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Posted: 6/29/2018 6:02:02 PM EDT
[#3]
Wouldn't that throw the engine off balance?
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Posted: 6/29/2018 6:04:46 PM EDT
[#4]
Quote HistoryQuoted:
Wouldn't that throw the engine off balance? |
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Posted: 6/29/2018 6:05:53 PM EDT
[#5]
I would do both sides OP.... sleds run high rpm's for long periods, a mis matched piston set is going to make issues down the road...
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Posted: 6/29/2018 6:07:15 PM EDT
[#6]
Thanks for the input guys
On somewhat of a budget. Doing 2 1980s Yamaha Phazers. |
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Posted: 6/29/2018 6:08:24 PM EDT
[#7]
Quote HistoryQuoted:
Wouldn't that throw the engine off balance? Cylinders won't breath the same If you stay 500 RPMs away from redline it might survive. Butis that what you want? |
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Posted: 6/29/2018 6:10:04 PM EDT
[#8]
Quote HistoryQuoted:
Thanks for the input guys On somewhat of a budget. Doing 2 1980s Yamaha Phazers. |
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Posted: 6/29/2018 6:10:29 PM EDT
[#9]
Wouldn't it make the carb difficult to adjust with one cylinder pulling a different volume of fuel/air mixture than the other?
Besides the balancing issues. Just thinking out loud. In for answers from those more experienced than I. |
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Posted: 6/29/2018 6:13:34 PM EDT
[#10]
Quoted:
Bought an old sled, guy said it needed the carbs cleaned. While cleaning them I noticed the oil tube had popped off and hadn't been oiled properly in who knows how long. So I get it apart (only 1800 miles), one piston looks good. One is a little scored on one side (the one that didn't have oil). So the plan is to over bore that one cylinder .020 over but I've never run into it where only one cylinder needed it. Can I just overbore one cylinder (new +.020 piston kit) and replace only the rings in the other one? I've read opposing view points on the internet, some saying its ok if I weight balance the pistons (remove some material from the oversize one). Thoughts? @AKSnowRider Over bore both. In cars, you overbore all cylinders if only one really needs it. |
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Posted: 6/29/2018 6:13:44 PM EDT
[#11]
Quote HistoryQuoted:
Wouldn't it make the carb difficult to adjust with one cylinder pulling a different volume of fuel/air mixture than the other? Besides the balancing issues. Just thinking out loud. In for answers from those more experienced than I. |
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Posted: 6/29/2018 6:14:54 PM EDT
[#12]
Quote HistoryQuoted: If the budget is that tight maybe just leave it? I guess that depends on how bad the scoring is. |
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Posted: 6/29/2018 6:15:07 PM EDT
[#13]
Quote HistoryQuoted:
Yeah, my thought as well. Parallel twin? Might put extra stress/wear on the crank, might vibrate more. Quote HistoryQuoted:
Quoted:
Wouldn't that throw the engine off balance? |
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Posted: 6/29/2018 6:19:48 PM EDT
[#14]
Quote HistoryQuoted: If it'll make a difference I'll spend the money. Sounds like its not worth risking it |
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Posted: 6/29/2018 6:20:37 PM EDT
[#15]
If the scoring is all vertical, very lightly hone to make sure there isn't any aluminum stuck to the bore and put a new piston and rings in it. It will run just fine like this.
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Posted: 6/29/2018 6:20:40 PM EDT
[#16]
Quote HistoryQuoted:
You can match the piston weights. Now he could have them bore the stock cylinder and insert a liner back to stock bore diameter, but would surely be both more work and cost then just boring both and buying pistons....He might hunt down a good used cylinder for cheaper then boring both, but I would still put new pistons in it because sleds run constant high rpm and are extremely hard on skirts..nothing worse then fixing one issue and have it blow up a month down the road because of an issue you ignored the first time thru it... |
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Posted: 6/29/2018 6:23:42 PM EDT
[#17]
Quote HistoryQuoted:
Yeah but still have to deal with all the issues the overbore causes with breathing, compression and flows..and heat for that matter.... Now he could have them bore the stock cylinder and insert a liner back to stock bore diameter, but would surely be both more work and cost then just boring both and buying pistons....He might hunt down a good used cylinder for cheaper then boring both, but I would still put new pistons in it because sleds run constant high rpm and are extremely hard on skirts..nothing worse then fixing one issue and have it blow up a month down the road because of an issue you ignored the first time thru it... Quote HistoryQuoted:
Quoted:
You can match the piston weights. Now he could have them bore the stock cylinder and insert a liner back to stock bore diameter, but would surely be both more work and cost then just boring both and buying pistons....He might hunt down a good used cylinder for cheaper then boring both, but I would still put new pistons in it because sleds run constant high rpm and are extremely hard on skirts..nothing worse then fixing one issue and have it blow up a month down the road because of an issue you ignored the first time thru it... Guy asked could he get away with it for a cheap assed build, which he probably could. I'm with you overall, spend another $100 and just punch both sides out |
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Posted: 6/29/2018 6:26:30 PM EDT
[#18]
Quote HistoryQuoted:
If the scoring is all vertical, very lightly hone to make sure there isn't any aluminum stuck to the bore and put a new piston and rings in it. It will run just fine like this. Gotta go tear the 2nd motor apart quick so I can place my order before the ebay 15% off ends  
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Posted: 6/29/2018 6:30:03 PM EDT
[#19]
Take the good piston a weight it, then take the new piston and weight it. Take the new one and trim some weight till you get it the same as the old piston is. .20 is not that much over size. Take a dermal and trim some weight out of the inside of the new piston. Now you can look around and you might beable to find a new piston that weights what your old piston weighs.
Wolf |
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Posted: 6/29/2018 6:31:44 PM EDT
[#20]
OP, what sleds?
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Posted: 6/29/2018 6:33:24 PM EDT
[#21]
You can balance that , just weight the pistons the same
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Posted: 6/29/2018 6:34:04 PM EDT
[#22]
Quote HistoryQuoted:
OP, what sleds? would be nice to avoid the overbore. Its $82 per cylinder to bore and hone at The Crank Shop, and $45 a piston (for cheap kimpex). Not a lot of money but I'm cheap
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Posted: 6/29/2018 6:38:03 PM EDT
[#23]
Quote HistoryQuoted:
Take the good piston a weight it, then take the new piston and weight it. Take the new one and trim some weight till you get it the same as the old piston is. .20 is not that much over size. Take a dermal and trim some weight out of the inside of the new piston. Now you can look around and you might beable to find a new piston that weights what your old piston weighs. Wolf  Attached File |
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Posted: 6/29/2018 6:39:15 PM EDT
[#24]
Quote HistoryQuoted: Sled in question is a 88 Yamaha Phazer. Also rebuilding an 89 so wondering if I run into the same thing. would be nice to avoid the overbore. Its $82 per cylinder to bore and hone at The Crank Shop, and $45 a piston (for cheap kimpex). Not a lot of money but I'm cheap |
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Posted: 6/29/2018 7:15:18 PM EDT
[#25]
Quote HistoryQuoted:
You have all summer, tear them down...most likely going to find one rough cylinder on each..mate the two good cylinders and bore the others Thanks for all the input guys! |
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Posted: 6/29/2018 7:19:08 PM EDT
[#26]
OP try walking around a whole day with a shoe one pound more than the other................. and ask this question again
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Posted: 6/29/2018 7:20:39 PM EDT
[#27]
If you're on a real tight budget, just weight match both pistons. Watch a couple YouTube videos on where to take the weight out of the new piston.
Myself, I would just put two new ones in. |
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Posted: 6/29/2018 7:24:29 PM EDT
[#28]
Quote HistoryQuoted: Just got the two cylinders off the other sled, looks like both need reboring. So I definitely need 3 out of 4, I'm thinking I may as well just do the 4th. Thanks for all the input guys! |
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Posted: 6/29/2018 7:26:12 PM EDT
[#29]
Get both.
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Posted: 6/29/2018 7:29:52 PM EDT
[#30]
Quote HistoryQuoted:
Number 1 cause on sleds for light scuffing pistons is lack of warm up time...People fire em up, let them warm for 5 minutes then jump on and hit full throttle... basically it causes the pistons to heat and swell faster then the cylinders do and it scuffs...We fire ours up, then go get dressed/packed up after 10-20 minutes we get on and run as little throttle as possible for the first 10-20 minutes..same deal when taking a 20 minute break on the hill..always park on tracks on flat ground or downhill and go easy for at least a few minutes until the temps equalize..a squirt of 2 stroke oil in every talk of gas isn't a bad thing either...especially on a rebuild for the first few tanks... 
I think its more of a deal with forged pistons. I run Wiseco forged pistons in my TRX250r, and the break in is a long elaborate process plus I have to let it slowly warm up each time I use it. My LTZ400 has cast pistons and Nicasil bore so its a little more forgiving. I only let it warm up a minute or two. |
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Posted: 6/29/2018 7:36:05 PM EDT
[#31]
Quote HistoryQuoted: I'm the same way, I go out and start my snowmobile, then come inside and suit up, let it warm up a good 10-15 minutes until the running boards are warm. Then I take it easy for the first 10 minutes. Pistons on the SRX700 that I took apart looked almost brand new (except for the pto side that got a mouse nest), I've owned it for about 10 years. The two phazers I bought over in NY for $600. In decent shape but I could tell when I bought them the guy didn't really take care of them. When he showed them to me, he fired them up and ripped on the throttle right as its first starting. I was like
I think its more of a deal with forged pistons. I run Wiseco forged pistons in my TRX250r, and the break in is a long elaborate process plus I have to let it slowly warm up each time I use it. My LTZ400 has cast pistons and Nicasil bore so its a little more forgiving. I only let it warm up a minute or two. 
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Posted: 6/29/2018 7:44:58 PM EDT
[#32]
So nobody is going to let the OP know that snowmobiles have engines......not motors
. well at least last time I checked the market for electric snowmobiles is pretty slim.
Yes my Friday drinking has already begun |
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Posted: 6/29/2018 9:57:11 PM EDT
[#33]
Quote HistoryQuoted:
It is a long fucking walk to the truck when its blows up again in the dead of winter.....The trailer is 11 miles past the furthest hills you can see in this pic....Let alone getting the sled back to the trailer.... https://www.AR15.Com/media/mediaFiles/404934/IMG_0278-591523.JPG 
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Posted: 6/29/2018 10:02:47 PM EDT
[#34]
.020"? Why the fuck not? You'll never feel it in the seat of your pants. Don't over think this shit.
AB |
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Posted: 6/29/2018 10:03:01 PM EDT
[#35]
Quote HistoryQuoted:
If the scoring is all vertical, very lightly hone to make sure there isn't any aluminum stuck to the bore and put a new piston and rings in it. It will run just fine like this. |
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Posted: 6/29/2018 10:09:56 PM EDT
[#36]
Quote HistoryQuoted: Awesome pic!!!  Attached FileOr a nice sunset....  Attached Filesunny day of fun...notice all the fuel...  Attached FileShowing the kids how to turn a sled....  Attached File |
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Posted: 6/30/2018 12:28:36 AM EDT
[#37]
Quote HistoryQuoted:
thanks...got a few... how about a full moon night... https://www.AR15.Com/media/mediaFiles/404934/blacktruck013-591854.JPG Or a nice sunset.... https://www.AR15.Com/media/mediaFiles/404934/IMG_0276-591855.JPG sunny day of fun...notice all the fuel... https://www.AR15.Com/media/mediaFiles/404934/Picture011Custom-591857.JPG Showing the kids how to turn a sled.... https://www.AR15.Com/media/mediaFiles/404934/blacktruck116_edited-591860.JPG Quote HistoryQuoted:
Quoted: Awesome pic!!! https://www.AR15.Com/media/mediaFiles/404934/blacktruck013-591854.JPG Or a nice sunset.... https://www.AR15.Com/media/mediaFiles/404934/IMG_0276-591855.JPG sunny day of fun...notice all the fuel... https://www.AR15.Com/media/mediaFiles/404934/Picture011Custom-591857.JPG Showing the kids how to turn a sled.... https://www.AR15.Com/media/mediaFiles/404934/blacktruck116_edited-591860.JPG 
Paradise. |
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Posted: 6/30/2018 12:30:20 AM EDT
[#38]
Agree with AKSR that the money spent is a function of how fucked you'll be if that motor/engine/power delivery system decides to give up the ghost at some point.
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Posted: 6/30/2018 12:33:00 AM EDT
[#39]
Just break the piston rings free and run it. It will be fine now that it's getting oil.
Cheaper and better than 2 different piston sizes |
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Posted: 6/30/2018 12:40:25 AM EDT
[#40]
Quote HistoryQuoted:
I was going to mention piston weights have to be the same. If you're doing this as a budget type thing go for it. There really isn't any more risk in doing it this way or the "correct" way. Sometimes even a properly built engine will scatter due to some anamoly or oversight. That said - unless rock-bottom budget, once it's setup to bore one cylinder shouldn't be too much work to do others, but it may be unnecessary. Maybe toss a coin? |
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Posted: 6/30/2018 12:47:47 AM EDT
[#41]
I see your doing them all.
Have a 94 Indy trail deluxe 488 fan cooled that only had one side bored out. Put a lot of hard miles on it after. Know of a bunch of others run the same way. |
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Posted: 6/30/2018 12:53:00 AM EDT
[#42]
90% of the hassle is breaking down the engine and reassembling it. Might as well do both.
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Posted: 6/30/2018 12:57:05 AM EDT
[#43]
Yeah if it was me, I would do both. A snowmobile/snow go/snow machine/whatever they call it in your A.O. is IMO something you need to be dependable as it can leave you in a world of frozen hurt if it goes down at the wrong time. Would do it right
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Posted: 6/30/2018 1:03:35 AM EDT
[#44]
I had a triple polaris motor pop a piston on a trip.i took to a local guy in mercer who had a ready to go+ .030 jug and piston to fit the polaris motor.he installed it and 6500 miles later,no ill effects..fwiw
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Posted: 6/30/2018 1:09:13 AM EDT
[#45]
That would be great to see and hear. It would sound like an old Jonny Popper.
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Posted: 6/30/2018 1:10:28 AM EDT
[#46]
Quote HistoryQuoted:
That would be great to see and hear. It would sound like an old Jonny Popper. 
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Posted: 6/30/2018 1:40:56 AM EDT
[#47]
Arfcom be all experts, but they aren't. Yes, you can bore one cylinder and it won't cause a problem. Won't be off balance, or breathe wrong or whatever the fuck else Arftards dream up. If you are using factory pistons, a .010, .020, .030, etc. should all weigh the same. That way when it is overbored and larger diameter piston installed it won't be off balance. Aftermarket, who knows. If the cylinder is not deeply scored you may be able to hone it to get it smoothed out and just put back in the stock piston, new one of course.
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Posted: 6/30/2018 4:09:31 AM EDT
[#48]
Quote HistoryQuoted:
You can balance that , just weight the pistons the same |
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Posted: 6/30/2018 5:04:28 AM EDT
[#49]
A .020 over or is fine on one cylinder. It's not even remotely close to that finely balanced from the factory. Don't worry about it a bit. The idea that a .020 over bore will alter AFR in any significant way is laughable.
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Posted: 6/30/2018 5:08:18 AM EDT
[#50]
Quote HistoryQuoted: Just got the two cylinders off the other sled, looks like both need reboring. So I definitely need 3 out of 4, I'm thinking I may as well just do the 4th. Thanks for all the input guys! |
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